1. Field of the Invention
This invention relates to a variable magnification projection device applicable for us in an electrophotographic copying machine (hereinafter referred to as a copier). More particularly, the invention concerns an improved variable magnification projection device having a fixed conjugate distance and composed of the combination of a principal lens displaceable within a certain range along the axis of its optical path and a supplementary lens movable into and out of the optical path with said displacement of the principal lens.
2. Description of the Prior Art
The following description is provided, by way of example only, in the context of a copier, although it will be recognized that the invention has a generally wider range of potential applications.
In a conventional variable magnification projection device of fixed conjugate distance for a copier, a supplementary lens is arranged for movement into and out of the optical axis of a principal lens. Typically, the principal lens is disposed for displacement along its optical axis within a fixed or certain range and the supplementary lens is hingedly supported and engaged through linkage with the displacement mechanism of the principal lens so that movement of the supplementary lens out of and into fixed variable magnification positions along the optical path is achieved; such a system may be seen in Japanese Patent Publication No. SHO-51-18812, while a similar arrangement in a lens shutter system of a camera is disclosed in U.S. Pat. No. 3,476,478. However, the details of construction of both such devices are complex, and problems arise in their adjustment and repair as a consequence of their complicated arrangements.
Futhermore, obtaining a change of magnification in such devices of greater than 3 steps requires at least two separate supplementary lenses in stacks or having a large variation in the distance between the principal lens and each supplementary lens and further complicates the construction, notably decreasing its durability and accuracy.